Dry cell structure and method for making the same



Oct 9, 1956 F. E. STEVENS, JR.. ET A1. 2,766,316

DRY CELL STRUCTURE AND METHOD FOR MAKING THE SAME Filed March 24 1955 44. A 3 I xx is INVENTORS 3 Franklyn E. Stevens, Jn

Russell A. Holmes ATTORNEYS United States Patent O DRY CELL STRUCTURE AND METHOD FOR MAKING THE SAM'E Franklyn E. Stevens, Jr., New Haven, and Russell A. Holmes, Hamden, Conn., assignors to Olin Matlneson Chemical Corporation, a corporation of Virginia Application March 24, 1953, Serial No. 344,402

4' Claims. (Cl. 13G- 133) This invention relates to dry cells, and more particularly concerns a dry cell construction which may be used in cells of the general type employed for powering flashlights and in similar applications. The invention also includes a method for assembling a seal for the cell Known dry cells of the type used, for example, in llashlights generally comprise an open topped can of zinc, which acts as the cell anode and a central carbon pencil protruding from the open end of the can, which acts as the cell cathode. Within the can, the cathode pencil is surrounded by a core of depolarizing mixture, usually comprising manganese dioxide and carbonaceous material, and an electrolyte, usually in the form of an aqueous paste fills the space between the depolarizing core and the zinc can. In conventional dry cell constructions, the open topped can is sealed by a layer of material capable of being softened and rendered lowable by heat, usually Wax.

The Wax seals of dry cells of the type described are unsatisfactory for several reasons. When subjected to moderately high temperatures, such as those encountered during storage in warm climates or seasons, the wax seals soften, with the result that water vapor escapes from the seal, the electrolyte becomes dehydrated, and the capacity and useful life of the cell are reduced. This loss of water vapor is aggravated by the fact that the hydrogen evolved within the cell forces its way out through the softened wax seal and carries water vapor with it. The softened wax may also be forced out around the -top seal of the cell and so renders the cell unmarketable.

With the foregoing in mind, it is proposed, in accordance with the present invention, to provide an improved dry cell which is capable of withstanding extended storage at elevated temperatures without substantial loss of capacity. More specically, the cell of the invention embodies a seal for the electrolyte, which is impervious r or substantially impervious to water vapor, is resistant to the electrolyte, is not softened or rendered pervious by any temperatures encountered in storage or use, and which is readily and inexpensively incorporated in the cell structure. According to one aspect of the invention, the improved seal is not only impervious to water vapor but is permeable to hydrogen to permit relief of hydrogen evolved within the cell without substantial loss of water from the electrolyte.

In describing the invention in detail, reference will be made to the accompanying drawings, in which an embodiment of the invention is illustrated.

In the drawings:

Fig. l is a sectional View of carbon pencil cathode and a sealing gasket or disc showing a method of assembling an embodiment of the invention;

Fig. 2 is a plan view of the sealing disc;

Fig. 3 is a partial sectional elevation of a dry cell incorporating the invention in the rst stage of assembly;

Fig. 4 is a view similar to Fig. 3, showing the cell in a subsequent stage of assembly; and

Price Fig. 5 is an elevation, partly in section, showing a com? pletely assembled dry cell embodying the invention.

Referring to the drawing, a zinc can of conventional of depolarizing mixture, usually manganese dioxide, and

a carbonaceous material, such as graphite, powdered carbon, and the like, and an aqueous electrolyte` paste 4 containing the usual electrolytes and lillinglthe space be` tween the depolarizing mixture core 3 andfthe'can l1.

In accordance with the invention, the upper end of the cell is sealed by means of a sealing gasket or disc S4 formed of what may be conveniently termed a rubber- More specifically, this material is` relike material. silient, resistant to the electrolyte of the cell, substantially impervious to water vapor, and preferably permeable to hydrogen. It is capable of withstanding temperatures encountered in storage and use of the cell. `Polyethylene, and particularly heat-resistant grades of polyethylene, comprise a preferred material for the sealing disc 5, but other materials, such as polytetrauoroethylene, polychlorotrifluoroethylene, natural rubber, rubbery vinyl copolymers, and rubbery vinylidene chloride c0- polymers may be employed.

The sealing disc 5 is circular and, before application to the cell, is of considerably greater diameterlthan the can 1, as is illustrated in Fig. 2.` The disci is` provided of the pencil 2 is illustrated in line 2.

In order to incorporate the sealing disc 5l in the cell-.lV structure, the disc is forced down over the protruding` l upper end of the carbon pencil 2` so that the pencil.` forces its way through the centralV disc `openings 6. v This l stretches `the resilient material of the disc and forms a short neck or sleeve 7 of the disc material :around the pencil Z and extending upwardly from the plane of the disc, as shown in Figs. 1 and 3. This sleeve 7 and the disc 5 tightly grip the carbon pencil 2 due to the resilience of the material from which the disc is formed. By this operation of forcing the disc over the upper end of the pencil, the outer edge of the disc 5 is bent upwardly into cupped form by the can top edge, as is illustrated in Fig. 3. A top closure 8 of a size to be received Within the open top end of the can 1 and having a central opening 14 to receive the carbon pencil 2 is then inserted in the top end of the can over the sealing disc 5. The closure 8 is formed of a suitable suibstantia'llyr rigid thermoplastic or thermosetting insulating material, such as polystyrene, phenol formaldehyde resin, or the like. The lower end of the 4central closure disc opening 14 is ared youtward slightly so that as the closure 8 is forced down over the carbon pencil 2, the upstanding sleeve 7 tof the sealing disc 5 is compressed between the closure K8 and the carbon pencil 2 to form a tight seal at this point. The closure 8 is provided with an annular groove 9 in its upper surface near its periph-- eral edge, and the top edge of the can 1, together with the edge of the sealing disc 5, is rolled inward to provide a firm roll crimp 10 which retains the disc 5 in place and tightly seals the can 1 to the disc 5 and the: closure 8. The usual metal contact cap 11 is then forced over the protruding outer end of the carbon pencil 2 and the assembly is complete, as shown in Fig. 5.

The cell constructed in accordance with the invention has the advantage that it does not dry out, lose is capacity lor lose its top sealing material even when stored at high temperatures for considerable periods, Its sealing parts are simple and easy to assemble.

(felis constructed V`according to the invention exhibit Vconsiderably greater capacity after storage at elevated temperatures than do conventional cells sealed with wax, pitch or like heat-flowable materials. lnV the tests of whichthe, results are tabulated below, each cell was stored for two Weeks at 160 F. In the tests et which the results are given inthe column designated A, each cell, after. such storage, was discharged through a resistance'of 62/4` ohms for a period of four minutes every thirty minutes for ten hours a day and ive days a week, until the cell voltage had dropped from the initiai value of 11/2 Volts t0 0.93 volt. YThe results are given in terms of total day-softest. In the tests of which the results are given in the column designated 13, each cell, after high temperature storage, was continuously discharged through a resistance of 831/3 ohms until the cell voltage had dropfpedtoV 1.13 volts. The results of test E are given in terms-of tot-al hours of the test. in the tests et which the results are givenin the column designated C,V the cells `were discharged through a resistance of ten ohms for four hours a day tive days a week until the cell voltage had dropped to 0.90 volt. The results of the test C are given in terms of the total hours cf discharge.

Cell Seal Test A, Test 13, Test 0, days hours hours Wax 6. 8 107 10. 4 Polyethylene Disc 11. 0 169 17. 8

We claim:

gases and a cupped edge porticn on the inner wall of the can, and a substantially rigid member arranged over the disc and compressively engaging the sleeve and the cupped edge portion of the disc.

2. A dry cell according to claim 1, in which the disc formed of a material selected `from the class consisting of polyethylene, polytetrafiuoroethylene, polychlorotrinoreethylene, natural rubber, rnbbery vinyl copolymers, rubbery vinylidene chloride copolymers.

3. A dry cell according to claim l, in which the disc td ci `polyethylene.

A closure for a dry cell comprising an open ended Zinc can and a centrally arranged carbon cathode pencil extending `from the open endV of the can, characterized in that the closure comprises a disc of resilient rubberlike material of greater diameter than the diameter of the can and having a central opening of smaller diameter than that of the carbon pencil forced downwardly over the pencil into the open mouth of the can `forming a sleeve surrounding the pencil and a cupped edge portion en the inner Wall of the can, a substantially rigid closure having a central aperture with a ilared lower mouth disposed within the open end of the can over said disc and having a groove on its outer surface adjacent its peripheral edge, the ared lower mouth of the closure aperture compressively engaging the sleeve of said disc and forcing it against said cathode pencil and a roll crimp at the open edge of said can compressively `forcing the edge of said disc into said closure groove.

References Cited in the le of this patent UNITED STATES PATENTS 

